But how does one develop OCD? The Mayo Clinic sites three main causes for obsessive compulsive disorder: biology, environment, and insufficient serotonin levels. All three are taken into consideration by doctors, psychotherapists and psychiatrists when diagnosing and treating OCD.

Theories Based on Environment

The thoughts and behaviors of someone suffering with OCD often center on the issues of aggression, counting, or cleanliness. For example, one might have recurring and intrusive thoughts that something is dangerous, or that everything around him is full of germs. A person might feel compelled to count everything he see--bricks on the sidewalk, for instance--in order for him to move on to the next activity.

A study reported in Behavioral Genetics, in March, 2008, looked at twin studies. One group of researchers found a clear correlation between childhood sexual abuse and OCD, again, suggesting environmental stress as a trigger for OCD.

A common belief is that those with OCD had mothers who punished them as a child for any level of disarray in their homes. Hence, as an adult, the person spends his life trying to avoid the offending situation, making sure everything is in its place. Scientists would also point out that there is a correlation between the parent having OCD and the child having OCD, which may reflect an environmental influence as well as a genetic one. Another theory comes from Sigmund Freud, the father of modern psychotherapy, who believed that the child is obsessed with acts of elimination. Freud hypothesized if this stage was interrupted, the person would remain in this stage, displaying unusual interest in cleanliness or violence.

University of Cambridge's Department of Psychiatry researchers (2008) using a functional MRI found that those with OCD and their families had less activity in a certain area of the brain. They found the lateral orbitofrontal cortex, in the frontal area of the brain, was less responsive than other areas. This implies a physiological difference as well as a possible genetic link. It has been established that people with OCD are more likely to have a family member with a similar anxiety disorder. However, this correlation could be caused by a genetic similarity, a similarity of environment, or family patterning behavior.

Other researchers have found other differences in the brain associated with OCD. The amygdala, the area of the brain that processes danger, has also been suggested as the root cause of OCD. Some studies have found differences in the amygdala in an OCD patient. Also implicated are the caudate nucleus and the thalamus. None of these studies are conclusive or exclusive.

Several studies have found a significant but not overwhelming increase in OCD among family members. The increase in likelihood of having OCD from one twin with the disorder to the other is slightly more than the family correlation, but does not suggest an OCD gene. Researchers have also found that there are slightly more females with OCD than men.

Theories Based on Serotonin Level

Serotonin is a neurotransmitter in the brain allowing the brain cells to communicate with each other. A study from the National Institutes of Health found that people with OCD responded positively to treatment with pharmacological agents, more specifically, selective seratonin reuptake inhibitors (SSRIs). These drugs work by making more serotonin available by blocking its reabsorption within the neural synapse.